Technical Field
This application relates to a vascular filter and more particularly to a method of inserting a vein filter into the vessel.
Background of Related Art
Passage of blood clots to the lungs is known as pulmonary embolism. These clots typically originate in the veins of the lower limbs and can migrate through the vascular system to the lungs where they can obstruct blood flow and therefore interfere with oxygenation of the blood. Pulmonary embolisms can also cause shock and even death.
In some instances, blood thinning medication, e.g. anticoagulants such as Heparin, or sodium warfarin can be given to the patient. These medications, however, have limited use since they may not be able to be administered to patients after surgery or stroke or given to patients with high risk of internal bleeding. Also, this medication approach is not always effective in preventing recurring blood clots.
To avoid invasive surgery, less invasive surgical techniques involving placement of a mechanical barrier in the inferior vena cava have been developed. These barriers are in the form of filters and are typically inserted through either the femoral vein in the patient's leg or the right jugular vein in the patient's neck or arm under local anesthesia. The filters are then advanced intravascularly to the inferior vena cava where they are expanded to block migration of the blood clots from the lower portion of the body to the heart and lungs.
These prior filters take various forms. One type of filter is composed of coiled wires such as disclosed in U.S. Pat. Nos. 5,893,869 and 6,059,825. Another type of filter consists of legs with free ends having anchors for embedding in the vessel wall to hold the filter. These filters are disclosed, for example, in U.S. Pat. Nos. 4,688,553, 4,781,173, 4,832,055, and 5,059,205, 5,984,947 and 6,007,558. Another type of filter is disclosed in U.S. Pat. No. 6,214,025 consisting of wires twisted together to form a cylindrical anchoring portion conforming to the inner vessel wall surface to exert a radial force and a conical filtering portion.
Commonly assigned U.S. Pat. No. 7,704,266 (the “266 patent”) and U.S. Pat. No. 8,162,972 (the “972 patent”), the entire contents of both of which are incorporated herein by reference, disclose other forms of vein filters. These filters can be permanently implanted or removed minimally invasively, e.g. intravascularly.
The methods of placement of the filter described in the '274 and '972 patents are effective. However, in certain patients, the vena cava is not straight, but is curved and/or more tortuous. Although the filters of the '274 patent and '972 patents can be placed effectively in such vena cava, it would be advantageous to provide a delivery method and apparatus to even better accommodate these curved anatomies.
Additionally, the better centered the filter, the easier the subsequent removal of the filter. This is due to the fact that if the retrieval end (cranial end) of the filter is against the vessel wall when placed, access to the retrieval end could be difficult. Also, additional tissue ingrowth could occur over the cranial end which could increase the difficulty of removal.
Prior art attempts to center the filter include modifications to the filter itself to provide centering structure. Not only does this complicate the filter design but could require the length of the filter to be increased. Such increased length can be disadvantageous due to limited space in the inferior vena cava.
Commonly assigned Patent Publication No. 2009/0143813 (Ser. No. 12/288,217, filed Oct. 17, 2008) discloses an attempt to center the filter without modifying the filter. In this patent publication, the delivery system is modified to provide for more centered placement of the filter by moving the delivery sheath opening toward a center of the vessel by use of a curved pusher. Although in certain applications this method has been effective, sometimes the user does not properly perform the technique and therefore the filter is not centered upon delivery.
Therefore, it would be advantageous to improve centered delivery of a filter within the vessel by modifications of the filter delivery system, rather than the filter itself, and which can provide a more reliable and consistent technique for centered placement.